Question

Here’s a little Brownian motion demo in WPF:

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Shapes;
using System.Windows.Threading;
using System.Threading;

namespace WpfBrownianMotion
{
    static class MiscUtils
    {
        public static double Clamp(this double n, int low, double high)
        {
            return Math.Min(Math.Max(n, low), high);
        }
    }

    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            Width = 500;
            Height = 500;

            var canvas = new Canvas();

            Content = canvas;

            var transform = new TranslateTransform(250, 250);

            var circle = new Ellipse()
            {
                Width = 25,
                Height = 25,
                Fill = Brushes.PowderBlue,
                RenderTransform = transform
            };

            canvas.Children.Add(circle);

            var random = new Random();

            var thread =
                new Thread(
                    () =>
                    {
                        while (true)
                        {
                            Dispatcher.Invoke(
                                DispatcherPriority.Normal,
                                (ThreadStart)delegate()
                                {
                                    transform.X += -1 + random.Next(3);
                                    transform.Y += -1 + random.Next(3);

                                    transform.X = transform.X.Clamp(0, 499);
                                    transform.Y = transform.Y.Clamp(0, 499);
                                });
                        }
                    });

            thread.Start();

            Closed += (s, e) => thread.Abort();
        }
    }
}

My question is this. In cases like this where the standard WPF animation facility isn’t being used, is the above approach using Thread and Dispatcher the recommended approach to take?

In general, I sometimes have states that need to be updated and rendered and the animation facility isn’t a good fit. So I need a way to do the update and rendering in a separate thread. Just wondering if the above approach is the Right Thing.

Answer 1

Clemens in the comments above suggested using DispatcherTimer. Indeed, this does simplify the code quite a bit. Here’s a version taking that approach:

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Shapes;
using System.Windows.Threading;

namespace WpfBrownianMotion
{
    static class MiscUtils
    {
        public static double Clamp(this double n, int low, double high)
        {
            return Math.Min(Math.Max(n, low), high);
        }
    }

    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            Width = 500;
            Height = 500;

            var canvas = new Canvas();

            Content = canvas;

            var transform = new TranslateTransform(250, 250);

            var circle = new Ellipse()
            {
                Width = 25,
                Height = 25,
                Fill = Brushes.PowderBlue,
                RenderTransform = transform
            };

            canvas.Children.Add(circle);

            var random = new Random();

            var timer = new DispatcherTimer();

            timer.Tick += (s, e) =>
                {
                    transform.X += -1 + random.Next(3);
                    transform.Y += -1 + random.Next(3);

                    transform.X = transform.X.Clamp(0, 499);
                    transform.Y = transform.Y.Clamp(0, 499);
                };

            timer.Start();
        }
    }
}